a. Field of the Invention
The present invention relates to a display device comprising a plurality of pixel elements and also to a method of inspecting such a display device.
b. Description of the Prior Art
Display devices typified by liquid crystal displays have several features, i.e., they have reduced device depth, are lightweight, and have low electric power consumption. By making use of these features, these display devices are used as displays for personal computers and word processors. Furthermore, these display devices are used as TV displays and as projection displays. In this way, display devices of this kind are used in various applications.
Among these display devices, an active matrix liquid crystal display having switching devices electrically connected with pixels has been earnestly researched and developed, because this liquid crystal display can accomplish good image quality, i.e., no crosstalk is produced between adjacent pixels.
The active matrix liquid crystal display comprises a liquid crystal panel consisting of a plurality of pixels, together with an X-driver circuit portion for supplying an analog image signal to the individual pixels of the liquid crystal panel. For example, this X-driver circuit portion comprises an X-printed wiring board and an X TAB (tape automated bonding) chip consisting of a signal line-driving IC installed on a flexible sheet. The X printed-wiring board supplies serial image data of several bits and a control signal to the X TAB chip. The output terminals of the X TAB chip are connected with the signal lines of the display panel via an anisotropic conductive film or the like. The input terminals of the X TAB chip are soldered or otherwise connected to the X printed-wiring board. The X-driving circuit portion converts serially input image data successively into a parallel form. The obtained digital signal is converted into an analog form. The resulting signal is changed into analog image signals for their respective pixels and supplied to the liquid crystal panel.
The active matrix liquid crystal display is further equipped with a Y-driver circuit portion for selecting the pixels on the display panel for each row. This Y-driver circuit portion also includes a Y TAB chip consisting of a Y-driving IC installed on a flexible film and a Y printed-wiring board for supplying control signals to the Y TAB chip. The output terminals of the Y TAB chip are connected with the display panel via an anisotropic conductive film or the like. The input terminals of the Y TAB chip are soldered or otherwise connected to the Y printed-wiring board.
c. Objects of the Invention
After the above-described display device has been completed, it is necessary to inspect it to ensure product quality. For example, the display device conveys a certain image which is visually or otherwise checked. In this way, one judges whether the finished product is acceptable or not. If the display device has a defect that can be remedied by exchanging one of the driving ICs, one of the printed-wiring boards, or other part with another, then the defective part is replaced. In this manner, the display device is repaired.
Although defects in the display panel or driving circuit portions of the prior art display devices could be identified by the state of the displayed image it has been difficult to ascertain the source of the defect, i.e., which of the driving ICs, the printed-wiring boards, and other driving circuit boards, is responsible for the defect. Therefore, it has taken very long time to repair the display device.